Ref HAL: hal-02428517_v1
Ref Arxiv: 2001.00912
DOI: 10.1103/PhysRevApplied.13.044079
WoS: 000529842800003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
1 Citation
Résumé:

We demonstrate that magnetic skyrmions with diameters around 60 nm can be stabilized at room temperature and zero external magnetic field in an exchange-biased Pt/Co/NiFe/IrMn multilayer stack. This is achieved through an advanced optimization of the multilayer stack composition in order to balance the different magnetic energies controlling the skyrmion size. Magnetic imaging is performed both with magnetic force microscopy and scanning Nitrogen-Vacancy magnetometry, the latter providing unambiguous measurements at zero external magnetic field. In such samples, we show that exchange bias provides an immunity of the skyrmion spin texture to moderate external magnetic field, in the tens of mT range, which is an important feature for applications as memory devices. These results establish exchange-biased multilayer stacks as a promising platform towards the effective realization of memory and logic devices based on magnetic skyrmions.

Commentaires: 5 pages, 3 figures

Ref HAL: hal-02302063_v1
DOI: 10.1016/j.diamond.2019.04.022
WoS: WOS:000474324600011
Exporter : BibTex | endNote
3 Citations
Résumé:

Control of the crystalline orientation of nitrogen-vacancy (NV) defects in diamond is here demonstrated by tuning the temperature of chemical vapor deposition (CVD) growth on a (113)-oriented diamond substrate. We show that preferential alignment of NV defects along the [111] axis is improved when the CVD growth temperature is decreased, leading to $79\%$ preferential orientation at 800°C, as compared to only 47.5% at 1000°C. This effect is then combined with temperature-dependent incorporation of NV defects during the CVD growth to obtain preferential alignment over dense ensembles of NV defects spatially localized in thin diamond layers. These results demonstrate that growth temperature can be exploited as an additional degree of freedom to engineer optimized diamond samples for quantum sensing applications.

Ref HAL: hal-02289672_v1
DOI: 10.1103/PhysRevMaterials.3.094001
WoS: 000483945800001
Exporter : BibTex | endNote
34 Citations
Résumé:

We study shallow and deep levels in carbon-doped hexagonal boron nitride crystals precipitated from a molten metal solution in a high-temperature furnace. Reflectance and photoluminescence under deep ultraviolet excitation are complemented by spatially resolved experiments by means of a scanning confocal micro-photoluminescence setup operating in the ultraviolet. Isotopically controlled carbon doping does not induce any energy shift of the well-known deep-level emission at 4.1 eV. Our detailed characterization in a series of carbon-doped crystals reveals that the incorporation of carbon during the growth process results in a distinct class of shallow and deep levels in hexagonal boron nitride, calling into question the exact role of carbon in the growth of hexagonal boron nitride and its direct or indirect influence on the formation of the crystal defects.

Ref HAL: hal-02100883_v1
DOI: 10.1103/PhysRevApplied.11.034066
WoS: WOS:000462958100004
Exporter : BibTex | endNote
7 Citations
Résumé:

We demonstrate room-temperature stabilization of dipolar magnetic skyrmions with diameters in the range of 100 nm in a single ultrathin layer of the Heusler alloy Co2FeAl (CFA) under moderate magnetic fields. Current-induced skyrmion dynamics in microwires is studied with a scanning nitrogen-vacancy magnetometer operating in the photoluminescence quenching mode. We first demonstrate skyrmion nucleation by spin-orbit torque and show that its efficiency can be significantly improved using tilted magnetic fields, an effect that is not specific to Heusler alloys and could be advantageous for future skyrmion-based devices. We then show that current-induced skyrmion motion remains limited by strong pinning effects, even though CFA is a magnetic material with a low magnetic damping parameter.

Ref HAL: hal-01920172_v1
Exporter : BibTex | endNote
Résumé:

Quantum sensing with diamond

Ref HAL: hal-01781380_v1
DOI: 10.1103/PhysRevMaterials.2.024406
WoS: WOS:000426041400004
Exporter : BibTex | endNote
19 Citations
Résumé:

Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a non-invasive, high resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including a static disorder, based on the physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media.

Ref HAL: hal-01768796_v1
DOI: 10.1088/1367-2630/aab574
WoS: 000428767400002
Exporter : BibTex | endNote
1 Citation
Résumé:

We analyze the properties of a pulsed coherent population trapping protocol that uses a controlled decay from the excited state in a Λ-level scheme. We study this problem analytically and numerically and find regimes where narrow transmission, absorption, or fluorescence spectral lines occur. We then look for optimal frequency measurements using these spectral features by computing the Allan deviation in the presence of ground state decoherence and show that the protocol is on a par with Ramsey-CPT. We discuss possible implementations with ensembles of alkali atoms and single ions and demonstrate that typical pulsed-CPT experiments that are realized on femto-second timescales can be implemented on micro-seconds timescales using this scheme.